This invention concerns a novel emulsifying agent and emulsified cosmetics using the same.
In the preparation of emulsified cosmetics, combination of higher fatty acid salts and nonionic surfactants have frequently been used as emulsifying agents therefor. However, although the emulsifying agent containing the higher fatty acid salt is excellent for attaining stable emulsification, presence of the higher fatty acid salt increases the pH value to render the cosmetic composition alkaline. By the way, the surfaces of human skins are normally covered with weakly acidic membrane (pH 4.5-6.5) and, upon contact with an alkaline substance, acidic substance is secreted to recover normal pH value of the membrane thereby maintaining its weakly acidic condition. Accordingly, it is desired that cosmetics such as creams and milky lotions applied to the skins are conditioned to weakly acidic or neutral pH.
In view of the foregoings, in the preparation of emulsified cosmetics using a higher fatty acid salt as the emulsifying agent, the addition amount of a basic substance (such as sodium hydroxide, potassium hydroxide and triethanolamine) used for neutralizing the higher fatty acid has been reduced extremely or an acidic pH buffer such as lactic acid--sodium lactate has been added after the preparation of the emulsified system, in order to reduce the pH value of the cosmetics. However, these methods are defective in that they provide poor emulsified state, which is destroyed with time to cause layer-like separation thereby significantly worsen the appearance of the cosmetics.
Further, a higher alcohol sulfate has also been used in place of the higher fatty acid salt but an emulsified system prepared therewith has a defect of giving excessively keen irritations to the skins, as well as being instable due to gradual hydrolysis of the higher alcohol sulfate with time, although the system is stable under weakly acidic or neutral conditions.
Furthermore, it has also been known that neutral or weakly acidic emulsified cosmetics can be obtained by the use of a nonionic surfactant as the emulsifying agent but, since the nonionic surfactant has only insufficient emulsifying power, it has to be used in a great amount thus causing undesirable feelings or the likes in actual use.